1. Field of the Invention
The present invention relates to an adhesive sheet for dicing. Further, the present invention relates to a method of dicing by using the adhesive sheet for dicing and to small cut pieces obtained by the dicing method. In case that small element pieces, such as semiconductor wafers cut and separate (dice), the adhesive sheet for dicing according to the present invention is particularly useful as an adhesive sheet for dicing semiconductor wafers, which is used for fixing materials to be cut, such as semiconductor wafers. For example, the adhesive sheet for dicing according to the present invention can be used as an adhesive sheet for dicing silicon semiconductors, an adhesive sheet for dicing compound semiconductor wafers, an adhesive sheet for dicing semiconductor packages, an adhesive sheet for dicing glass, and the like.
2. Description of the Related Art
Conventionally, a semiconductor wafer made of silicon, gallium or arsenic is produced in a state having a large diameter, then cut and separated (diced) into small element pieces, and transferred to a mounting step. In this process, the semiconductor wafer is subjected, in a state maintained by sticking on an adhesive sheet, to the respective steps such as a dicing step, a washing step, an expanding step, a pick-up step and a mounting step. As the adhesive sheet, a sheet including an acrylic series adhesive of about 1 to 200 μm in thickness applied onto a base material consisting of a plastic film is generally used.
In the dicing step, the wafer is cut with a rotating and moving circular blade, but a cutting system called full cutting where the base material of the adhesive sheet for dicing maintained the semiconductor wafer is cut into an inside of the base material, is a mainstream. Since the adhesive sheet is cut into an inside thereof by the full-cutting method, the base material i.e. a plastic film generates fibrous off-cuts. When the fibrous off-cuts adhere to the side of the chip (cut piece), the adhering fibrous off-cuts are mounted and contained in the chip in later steps, to cause a problem of a significant reduction in the reliability of the resultant semiconductor element. In the pickup step, individual chips are picked up after positioning under recognition with a CCD camera, but if there are fibrous off-cuts, there is also an inconvenience that a recognition error is caused.
As a means of solving such problems, for example Japanese Patent Application Laid-Open No. 156214 (1993) proposes an adhesive sheet using an ethylene-methacrylate copolymer as the base material. This adhesive sheet achieves a certain reduction in generation of fibrous off-cuts, but is not satisfactorily endurable in the dicing step in producing highly reliable semiconductors.
Further, Japanese Patent Application Laid-Open No. 211234(1993) proposes an adhesive sheet using a film irradiated with electron rays or radiations such as γ-rays at 1 to 80 MRad. However, this adhesive sheet is severely damaged by irradiation with radiations, thus hardly providing a film excellent in outward appearance and significantly costing in film production, and is thus not preferable in respect of quality level and costs.
A wafer is completely cut in the cutting method by full-cutting, and thus the quality level of the cut is varied depending on the adhesive sheet for dicing used. For example, in recent years as a wafer is thinned, a crack called chipping occurs on the back surface of the wafer, caused a serious problem of a reduction in the anti-bending strength of the wafer.
As a means of solving such problems, for example Japanese Patent Application Laid-Open No.335411(1993) proposes a method of producing a thinned semiconductor element (by conducting dicing first) wherein a semiconductor wafer with an element formed thereon is first subjected to dicing to form a groove of predetermined depth and then subjected to back-grinding to the depth of the diced groove. In this method, occurrence of chipping can be prevented, but since a semiconductor wafer is provided previously with a cut of dozens to hundreds μm in depth by dicing, there arises problems such as cracking prior to the back-grinding step and contamination of the surface of the wafer with grinding water from the groove in the back-grinding step, thus leading to a reduction in the yield of the semiconductor wafer.